BST begins at 01:00 GMT on the last Sunday of March and ends at 01:00 GMT (02:00 BST) on the last Sunday of October. Since 22 October 1995 the times of commencement and cessation of daylight saving time across the European Union have been aligned[3] – for instance Central European Summer Time begins and ends on the same Sundays at exactly the same time (that is, 02:00 CET, which is 01:00 GMT). Between 1972 and 1995, BST began and ended at 02:00 GMT and not on Easter Sunday.[4]

The following table lists recent past and near future starting and ending dates of British Summer Time:[5]

British Summer Time was first established by the Summer Time Act 1916, after a campaign by builder William Willett. His original proposal was to move the clocks forward by 80 minutes, in 20-minute weekly steps on Sundays in April and by the reverse procedure in September.[6] In 1916 BST began on 21 May and ended on 1 October.[7] Willett never got to see his idea implemented as he died in early 1915.

In 1940, during the Second World War, the clocks in Britain were not put back by an hour at the end of Summer Time. In subsequent years, clocks continued to be advanced by one hour each spring and put back by an hour each autumn until July 1945. During these summers, therefore, Britain was two hours ahead of GMT and operating on British Double Summer Time (BDST). The clocks were brought back in line with GMT at the end of summer in 1945. In 1947, due to severe fuel shortages, clocks were advanced by one hour on two occasions during the spring, and put back by one hour on two occasions during the autumn, meaning that Britain was back on BDST during that summer.[8][not in citation given]

An inquiry during the winter of 1959–60, in which 180 national organisations were consulted, revealed a slight preference for a change to all-year GMT+1, but the length of summer time was extended as a trial rather than the domestic use of Greenwich Mean Time abolished.[9] A further inquiry during 1966–67 led the government of Harold Wilson to introduce the British Standard Time experiment, with Britain remaining on GMT+1 throughout the year. This took place between 27 October 1968 and 31 October 1971, when there was a reversion to the previous arrangement.

Analysis of accident data for the first two years of the experiment, published by HMSO in October 1970, indicated that while there had been an increase in casualties in the morning, there had been a substantially greater decrease in casualties in the evening, with a total of around 2,500 fewer people killed and seriously injured during the first two winters of the experiment,[10][11] at a time when about 1,000 people a day were killed or injured on the roads.[12][13] However the period coincided with the introduction of Drink-Driving legislation, and the estimates were later modified downwards in 1989.[11]

The trial was the subject of a House of Commons debate on 2 December 1970[14] when, on a free vote, the House of Commons voted by 366 to 81 votes to end the experiment.[15]

Campaigners, including the Royal Society for the Prevention of Accidents (RoSPA) and environmental campaigners 10:10, have made recommendations that British Summer Time be maintained during the winter months, and that a "double summertime" be applied to the current British Summer Time period, putting the UK one hour ahead of GMT during winter, and two hours ahead during summer. This proposal is referred to as "Single/Double Summer Time" (SDST), and would effectively mean the UK adopting the same time zone as European countries such as France, Germany, and mainland Spain (Central European Time and Central European Summer Time).

RoSPA suggests this would reduce the number of accidents over this period as a result of the lighter evenings. RoSPA have called for the 1968–71 trial to be repeated with modern evaluation methods.[16]

While 10:10 generally agree with the safety benefits, their Lighter Later campaign focuses on the potential energy benefits of Single/Double Summer Time, arguing that the change could "save almost 500,000 tonnes of CO2 each year, equivalent to taking 185,000 cars off the road permanently".[17]

These proposals are opposed by some farmers and other outdoor workers, and many residents of Scotland and Northern Ireland,[18] as it would mean that, in northern Britain and Northern Ireland, the winter sunrise would not occur until 10:00 or even later. However in March 2010 the National Farmers Union indicated that it was not against Single/Double Summer Time and is in fact relatively neutral, with many farmers expressing a preference for the change.[19] Other opponents of daylight saving measures say that darker mornings, especially in Scotland, could have an impact on children going to school and people travelling to work.

Others have proposed the abolition of BST entirely, favouring GMT all year round. Advocates cite in their support a lack of practical gains from the adjustment of time, arguing instead that changes in school and/or business hours would achieve similar results without disrupting a scientific standard.

This period was stipulated by a Directive (2000/84/EC) of the European Parliament which required European countries to implement a common summer time (as originally introduced in 1997, in Directive 97/44/EC).[21]

In part because of Britain's latitudinal length, debate emerges most years over the applicability of BST, and is the subject of parliamentary debate. In 2004, English MP Nigel Beard tabled a Private Member's Bill in the House of Commons proposing that England and Wales should be able to determine their own time independently of Scotland and Northern Ireland. If it had been passed into law, this bill could have given the United Kingdom two different timezones for the first time since the abolition of Dublin Mean Time (25 minutes behind Greenwich) on 23 August 1916.

In 2005, Lord Tanlaw introduced the Lighter Evenings (Experiment) Bill[22] into the House of Lords, which would advance winter and summer time by one hour for a three-year trial period at the discretion of "devolved bodies", allowing Scotland and Northern Ireland the option not to take part. The proposal was opposed by the government. The bill received its second reading on 24 March 2006; however, it did not pass into law.[23] The Local Government Association has also called for such a trial.[24]

The Daylight Saving Bill 2010–12, a private member's bill by Conservative backbench MP Rebecca Harris, would have required the Government to conduct an analysis of the potential costs and benefits of advancing time by one hour for all, or part of, the year. If the analysis found that a clock change would benefit the UK, the bill required that the Government initiate a trial clock change to determine the full effects.[25]

In 2010, Prime Minister David Cameron stated he would seriously consider proposals in the bill. The bill was only likely to be passed with Government support. Despite initial opposition in Scotland to the move, Cameron stated his preference was for the change to apply across the United Kingdom, stating "We are a United Kingdom. I want us to have a united time zone."[26] A survey in late October 2010 of about 3,000 people for British energy firm npower suggested that a narrow majority of Scots may be in favour of this change, though the Scottish Government remained opposed.[27]

The bill was debated again in Parliament in November 2011 and sent to committee in December 2011.[28] In January 2012, the bill was again debated on the floor of the House of Commons where it was filibustered out of Parliament by opponents.[29]Angus MacNeil, MP for Na h-Eileanan an Iar, argued that it would adversely affect the population of Northern Scotland, while Jacob Rees-Mogg, MP for North East Somerset, tried to introduce an amendment to give Somerset its own time zone, 15 minutes behind London, in order to highlight what he saw as the absurdities of the bill.[30][31] With all its allocated time used up, the bill could proceed no further through Parliament.[32]